Process for producing ethylbenzene

ABSTRACT

A process for producing ethylated benzene by a reaction of benzene with ethylene in the presence of a catalyst containing a zeolite β by using a fixed-bed ascending-flow type reactor, which comprises 
     a) carrying out the reaction under conditions under which ethylene bubbles are present at the inlet of a catalyst layer when ethylene is fed upward from under the catalyst layer, 
     b) recovering reaction products as a liquid from the upper part of the reactor and at the same time taking out a distillate composed mainly of unreacted benzene therefrom as vapor, and 
     c) adjusting the temperature of the catalyst layer at its inlet to a temperature at least 50° C. lower than the maximum attained temperature of the catalyst layer.

This application is the national phase under 35 U.S.C. §371 of prior PCTInternational Application No. PCT/JP97/02476 which has an Internationalfiling date of Jul. 17, 1997 which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a process for producing ethylbenzeneuseful as, for example, a starting material for various polymers.

BACKGROUND ART

WO96/20148 discloses a production process of ethylbenzene from benzeneand ethylene using a zeolite such as MCM-22, MCM-49 or MCM-56 as ahighly selective catalyst. According to this reference, the alkylationis carried out in a liquid phase and the benzene/ethylenemolar ratio is5 to 10 in most cases and is 5.5 in the Examples.

U.S. Pat. No. 5,334,795 also discloses a synthetic process ofethylbenzene from benzene and ethylene using MCM-22 zeolite. However, inthe Examples of this reference, the benzene/ethylene molar ratio is atleast 4.6.

JP-B-06043346 discloses a process comprising bringing an organicaromatic compound into contact with a C2˜C20 olefin to form alkylationproducts in a distillation column reactor containing a structureobtained by immobilizing a fixed-bed acidic catalyst in a packing fordistillation, separating the formed alkylation products and unreactedorganic aromatic compound and olefin, and taking out the alkylationproducts from the distillation reactor at a place under the fixed bed.This reference, however, does not disclose employment of a β zeolite.Moreover, in the Examples of the reference, the benzene/ethylene molarratio of the reaction products recovered from the bottom is at least3.47 and the production rate of ethylbenzene relative to the weight ofthe catalyst is as very low as 0.12 to 0.3.

U.S. Pat. No. 5,118,896 discloses a process in which continuousliquid-phase alkylation of a liquid aromatic compound selected frombenzene, toluene and xylene using an olefin as an alkylating agent iscarried out in the fixed bed of a reactive-distillation type reactor byusing a catalyst comprising a crystalline aluminosilicatezeolite, silicaand alumina and having a pore volume of 0.25 to 0.35 ml/g, a pore radiusof more than 450 Å and aparticle diameter of not more than 1/64 inch.This reference describes an example using a reactive distillation methodin which the molar ratio of the aromatic compound to ethylene is 2. Inthis example, the conversion of ethylene is as very low as 55%.

JP-A-04187647 discloses a process in which alkylation andtransalkylation are carried out together on a molecular sieve catalystfor aromatic alkylation and transalkylation in a liquid phase, and thebenzene/ethylene molar ratio is 4 or less and may be about 2. In thisreference, a β zeolite is mentioned as the catalyst for alkylation andthe benzene/ethylene molar ratio is 5.2 in the Examples. The referencediscloses a method for attaining a benzene/ethylene molar ratio of 2under idealized reaction conditions. However, in this method, the abovemolar ratio value is attained by feeding ethylene in five stages.

WO96-04225 discloses fixed-bed liquid-phase alkylation by gas-liquiddescent parallel-flow method carried out in a trickle bed region by theuse of a β zeolite as a catalyst. However, this process has a highproductivity but is disadvantageous in that the catalytic activity isgreatly changed in the initial stage of the reaction and is difficult tocontrol.

JP-A-03181424 discloses liquid-phase alkylation and transalkylationwhich use a β zeolite as a catalyst, and the molar ratio of an aromatichydrocarbon to an olefin is 4 or more in the Examples of this reference.

Zeolite catalysts are used as catalysts for alkylation of aromatichydrocarbons and can be advantageously used as non-corrosive catalystsin place of the conventional catalysts for Friedel-Crafts reaction.Therefore, various proposals have been put forward for the zeolitecatalysts.

However, in most conventional processes, alkylation is carried out at arelatively high benzene/ethylene molar ratio. Since such a high molarratio increases the amount of unreacted benzene to be recycled and hencethe trouble of benzene recovery, it is very disadvantageous from anindustrial viewpoint. The reasons why alkylation is carried out at ahigh benzene/ethylene molar ratio in the conventional processes in spiteof the above fact are the following three reasons.

The first reason is the limitation of catalytic capability, i.e., a lowselectivity of nuclear ethylation. For example, Y type zeolites havebeen most widely used as alkylation catalysts. The Y type zeolites havebeen known to give a satisfactory activity and a good selectivity of adesired product but have been unusable by any means at a lowbenzene/ethylene molar ratio because it was found that at such a lowbenzene/ethylene molar ratio, the production of by-products such asbutylbenzene and diphenylethane becomes remarkable with an increase ofthe conversion of benzene, resulting in a markedly decreased selectivityof nuclear ethylation.

The second reason is that in the reaction carried out at a lowbenzene/ethylene molar ratio under a relatively low pressure byone-stage feed, ethylene exists as bubbles substantially at the inlet ofa catalyst layer, so that the activity of the catalyst is markedlydecreased. For example, JP-A-04187647 discloses employment of a Yzeolite as a transalkylation catalyst and describes the fact that whentransalkylation of diethylbenzene was carried out using the Y zeolytecatalyst in a trickle bed reactor substantially containing a gas phase,the conversion of diethylbenzene was markedly decreased in several hoursto 24 hours.

As a result of investigation by the present inventors, the following wasfound: when benzene is ethylated by a fixed-bed ascending-flow methodusing a Y type zeolite, at a low benzene/ethylene molar ratio under arelatively low pressure, the selectivity of nuclear ethylation is verylow and the activity is markedly decreased. It was confirmed that alsoin a batch reaction using a Y type zeolite, the selectivity and theactivity are markedly decreased with an increase of the conversion ofbenzene. It is conjectured that this decrease is due to the porousstructure of the Y type zeolite. That is, when there are compared the Ytype zeolite and a β zeolite which have the same oxygen-containing12-membered structure, the Y type zeolite has large cavities calledsuper-cages at the intersections of pores. It can be speculated that theproduction of binuclear products (e.g. diphenylethane) as by-productsbecomes easy in the cavities and causes the decrease of the selectivityand the clogging of the pores with high-molecular weight substances(i.e. the decrease of the activity) at the same time.

JP-A-06508817 discloses alkylation using as a catalyst a mordenite typezeolite having a silica/alumina molar ratio of more than 160 and anindex of symmetry of at least 1. The alkylation is carried out in areactor containing substantially no gas. Most preferably, it is carriedout in a completely liquid phase. The reference describes the fact thatthe substantial presence of a gas causes accumulation of an alkylatingagent in the gas to polymerize the alkylating agent, so that thedecrease of the selectivity and the inactivation of the catalyst areaccelerated. That is, the reference describes the impossibility ofcarrying out the alkylation using the above-mentioned mordenite typezeolite as a catalyst in a gas-liquid mixed phase substantiallycontaining ethylene bubbles.

Also in the case of MCM-22, MCM-49 and MCM-56 zeolite catalysts, thehighly selective catalysts disclosed in WO96/20148, etc., thebenzene/ethylene molar ratio is at least 4.6 as described above andmoreover this value could be attained only by multi-stage feed ofethylene to be completely dissolved. That is, for inhibiting thedeterioration of the catalytic activity, the reaction can be carried outonly under conditions under which ethylene is completely soluble inbenzene.

For using the above-mentioned catalyst, complete dissolution of ethylenein benzene is necessary. For carrying out the reaction at a lowbenzene/ethylene molar ratio, multi-stage feed of ethylene or a highpressure for increasing the solubility would be necessary. Therefore, ahigher pressure and a higher-order multi-stage feed are required forutilizing low-purity crude ethylene as a starting material, so thatethylene purification becomes indispensable. Thus, the above-mentionedcatalyst is not industrially usable in practice.

The third reason is a problem of removing the heat of reaction. Sincethe reaction is an exothermic reaction, heat is markedly generated whenthe reaction is completed at a low benzene/ethylene molar ratio. Therise of the temperature of a catalyst layer caused by the heatgeneration lowers the selectivity of alkylation, and if a liquid phasecannot be maintained, a remarkable decrease of the catalytic activitycannot be avoided. The removal of the heat of reaction is an importantproblem, and in conventional processes, alkylation has been unavoidablycarried out in the presence of a large excess of benzene (at a highbenzene/ethylene molar ratio) also from the viewpoint of the heatremoval.

In such circumstances, there has been proposed a method for solving theproblem of removing the heat of reaction, in order to achieve alkylationat a low benzene/ethylene molar ratio.

JP-A-04502451 or JP-A-04187647 has proposed a method for multi-stagefeed of ethylene. However, an apparatus for the multi-stage feed iscomplicated, and even when the multi-stage feed was conducted,alkylation is carried out at a high benzene/ethylene molar ratio of 3 ormore in Examples of the reference. For example, JP-A-04502451 describesthe following: benzene is fed to the first reaction zone of analkylation reactor having at least two reaction zones and a fresh olefinis fed to the entrance of each zone to carry out alkylation, whereby thebenzene/olefin molar ratio in the whole reactor is reduced whilemaintaining the benzene/olefin molar ratio in each zone at asufficiently high value to prevent the temperature rise, and thus atemperature rise to an abnormal temperature is avoided, resulting in animproved selectivity and an extended life of a catalyst. The referencedescribes the fact that since the reaction is carried out at a lowtemperature, a zeolite catalyst can be held in a liquid phase, so that atime required for the regeneration of the catalyst to become necessarycan be extended.

WO96/20148 discloses a process using MCM-22, MCM-49 or MCM-56 zeolite asa catalyst. According to this process, an olefin is fed in multiplestages and the heat of reaction is removed by providing one or morestages of cooling. This reference describes the fact that practice ofthe process at a substantially constant temperature increases the purityof the product and the life of the catalyst.

When such a process is employed, the number of stages of ethylene feedand the number of stages of cooling should be increased for attaining alower benzene/ethylene molar ratio, resulting in a complicatedapparatus.

On the other hand, there has also been proposed a process in which theheat of reaction is removed as a latent heat for evaporation by carryingout reactive distillation. For example, in the above referenceJP-B-06043346, a Y type zeolite as a catalyst is wrapped in cloth andpacked in the reactor. The products are recovered from the bottom of thereactor. Since the Y type zeolite catalyst is markedly deteriorated inactivity in the presence of substantially gaseous ethylene, the contactbetween the catalyst and ethylene bubbles is avoided by the use of thecloth and it can be speculated that ethylene is in a substantiallycompletely dissolved state in the reaction zone. However, when a Y typezeolite is used as a catalyst, it is by no means easy to carry out thereaction at a low benzene/ethylene molar ratio, also from the viewpointof maintaining the selectivity. In practice, the lowest benzene/ethylenemolar ratio of the products obtained from the bottom is at least 3.47 inthe Examples of JP-B-06043346. In such a reactive distillation method,since gaseous ethylene forms a continuous phase and moreover there isemployed a catalyst packing method which avoids the contact between thecatalyst and ethylene bubbles, complete conversion of ethylene isconsidered impossible as a matter of course.

U.S. Pat. No. 5,118,896 also discloses a reactive distillation methodand mentions employment of a β zeolite as a catalyst. However, onlyethylation of toluene by the use of a Y type zeolite is described in theExamples of this reference, and in the Examples using reactivedistillation, the catalyst is used wrapped in cloth. Therefore, also inthese Examples, ethylene bubbles are shut off from a catalyst, so that auniform liquid phase is maintained in a reaction zone. In this case, thearea of gas-liquid interface is inevitably the surface area of the clothand hence cannot be large. Therefore, a considerable number of stages (aconsiderable amount of the catalyst) is necessary for completing theconversion of ethylene, so that the productivity relative to thecatalyst would be low. In practice, in the Examples of the reference,the conversion of ethylene is only 55% under the following conditions;(toluene+benzene)/ethylene molar ratio: 2, catalyst weight: 272 g, feedrate of toluene: 151 g/Hr, feed rate of benzene: 27 g/Hr. In addition,carrying out the reaction by the reactive distillation method describedabove is dis-advantageous in that fixation of the catalyst layer in areactor is difficult, resulting in a complicated apparatus.

The same reference U.S. Pat. No. 5,118,896 describes ethylation oftoluene by the use of a Y type zeolite by a fixed-bed ascending-flowgas-liquid mixed-phase method using ethylene diluted with methane as astarting material, as an experiment for evaluating the catalyst.However, in this case, a catalyst layer is maintained at a constanttemperature with a divided electric furnace. In such a reaction method,even if a β zeolite is used as a catalyst in place of the Y typezeolite, complete conversion of ethylene cannot be achieved and thecatalyst is markedly deteriorated in activity. The reason is as follows:the starting liquid components are evaporated from the inlet of thecatalyst layer at a high temperature and the solubility of ethylene atthe inlet of the catalyst layer is decreased, so that the reactioncannot be completed; and the higher the temperature, the more remarkablethe deterioration in activity of the catalyst in the presence of gaseousethylene. Examples of the above reference are only intended to evaluatethe catalyst and no long-term operation was carried out therein. Inthese Examples, even short-term operation resulted in a decrease of thecatalytic activity, and no complete conversion of ethylene was achieved.

As described above, in the conventional processes, the reaction iscarried out in a complete dissolution system in order to preventsubstantially the presence of ethylene bubbles at least in a reactionzone, in view of the capability of a catalyst (the selectivity), thedecrease of activity of the catalyst, and the removal of the heat ofreaction. That is, there has been no choice but to carry out thereaction at a high benzene/ethylene molar ratio.

In such circumstances, when an industrially advantageous lowbenzene/ethylene molar ratio is desired, the reaction should be carriedout under a very high pressure, for example, for attaining the lowbenzene/ethylene molar ratio in one stage in a complete dissolutionsystem. Therefore, in the conventional processes, there is no choice butto employ a method comprising multi-stage feed of ethylene. Since thereis also a problem of removing the generated heat of reaction, a heatexchanger should be provided. If the heat of reaction is not removed,the temperature of a catalyst layer is raised, so that the solubility ofethylene would be further decreased. For carrying out the reaction in acomplete dissolution system, starting ethylene is required to have ahigh purity and hence ethylene purification is absolutely necessary.This is because a higher pressure is required for using diluted ethyleneas a starting material.

On the other hand, there have often been proposed so-calledreactive-distillation type reactors in which latent heat of evaporationis utilized for removing the heat of reaction. However, also in theactual reaction zone of such a reactor, ethylene should be completelydissolved and avoidance of the contact between a catalyst and ethylenebubbles is important, resulting in a complicated apparatus and acomplicated method for packing the catalyst. Moreover, since completeconversion of ethylene is impossible in principle, a finishing reactoris necessary for converting the residual ethylene as much as possible.Such demands on an apparatus pose an important problem in industrialproduction.

DISCLOSURE OF THE INVENTION

The present inventors earnestly investigated in order to solve theproblems described above, and consequently found that when there isemployed a process for producing ethylbenzene from benzene and ethylenein the presence of a catalyst containing a zeolite β by using afixed-bed ascending-flow type reactor, wherein

a) the reaction is carried out under conditions under which ethylenebubbles are present at the inlet of a catalyst layer when ethylene isfed upward from under a catalyst layer,

b) simultaneously with the recovery of the reaction products as a liquidfrom the upper part of the reactor, a distillate composed mainly ofunreacted benzene is taken out therefrom as vapor, and

c) the temperature of the catalyst layer at its inlet is adjusted to atemperature at least 50° C. lower than the maximum attained temperatureof the catalyst layer,

it becomes possible even at a very low benzene/ethylene molar ratio toremove the generated heat of reaction easily and suppress the abnormalrise of the temperature of the catalyst layer, so that ethylated benzenecan be produced in very high yield with high selectivity. On the basisof the above finding, the present invention has been accomplished.According to the present invention, ethylene can be completelyconverted, the decrease in activity of the catalyst can be suppressed,and the reaction can be carried out at a low benzene/ethylene molarratio under a low pressure by the use of a simple apparatus.

The present invention is a process for producing ethylbenzene frombenzene and ethylene in the presence of a catalyst containing zeolite βby using a fixed-bed ascending-flow type reactor, wherein

a) the reaction is carried out under conditions under which ethylenebubbles are present at the inlet of a catalyst layer when ethylene isfed upward from under the catalyst layer,

b) simultaneously with the recovery of the reaction products as a liquidfrom the upper part of the reactor, a distillate composed mainly ofunreacted benzene is taken out therefrom as vapor, and

c) the temperature of the catalyst layer at its inlet is adjusted to atemperature at least 50° C. lower than the maximum attained temperatureof the catalyst layer.

BEST MODE FOR CARRYING OUT THE INVENTION

The catalyst used in the present invention is a zeolite β. Zeolites βare synthetic crystalline aluminosilicates disclosed for the first timein U.S. Pat. No. 3,308,069 and are identified by their characteristicX-ray diffraction patterns described in this reference. Table 1 showsreflection d values obtained for the zeolites β in X-ray diffraction.

                  TABLE 1                                                         ______________________________________                                        Reflection d values for β zeolites                                       ______________________________________                                        11.4 ± 0.2 Å                                                             7.4 ± 0.2                                                                  6.7 ± 0.2                                                                  4.25 ± 0.1                                                                 3.97 ± 0.1                                                                 3.0 ± 0.1                                                                  2.2 ± 0.1                                                                ______________________________________                                    

The SiO₂ /Al₂ O₃ ratio of the zeolite β used in the present invention is5 to 100, preferably 10 to 80, more preferably 15 to 40.

The zeolite β used as a catalyst in the present invention is preferablyso-called acid type zeolite β obtained by replacing sodium ions byhydrogen ions and/or polyvalent cations by ion exchange. A zeolite βhaving a sufficient organic cations/sodium ions ratio can be used afteronly calcination. For attaining a higher activity, it is preferable toconvert a zeolite β to a hydrogen ion type by ion exchange. The ionexchange into the hydrogen ion type is preferably carried out by thefollowing method.

A synthesized zeolite β is calcined to be freed of organic substances,and then stirred in a dilute aqueous nitric acid solution to besubjected to ion exchange into a hydrogen ion type, which is dried to befreed of water so that the amount of water contained therein may be 10parts by weight or less, and the dried product is used for the reaction.

In packing the catalyst into the reactor, the catalyst is preferably ashaped or molded article. For obtaining the shaped or molded article,there may be shaped or molded either a pure zeolite or a zeolitecontaining one or more inorganic oxides (e.g. alumina, silica,silica/alumina or natural clay) as a binder(s). As a shaping or moldingmethod, tableting, extrusion, etc. are well known in the art. The shapeof the shaped or molded catalyst is generally cylindrical. For example,spherical, plate-like or hollow-and-cylindrical shaped or moldedarticles are also used.

The mode of reaction in the present invention is a fixed-bedascending-flow reaction mode. The catalyst shaped or molded product ispacked into the reactor. Benzene, a reactive material is introduced intothe reactor through the lower part of the reactor after being preheatedto a predetermined temperature 50° C. lower than the maximum attainedtemperature of the catalyst layer. On the other hand, ethylene is alsointroduced into the lower part of the reactor or the catalyst layer.Since the reactor is heat-insulating and the reaction is exothermic,heat is generated as the reaction proceeds, so that the liquidtemperature (the temperature of the catalyst layer) rises. However,since the operating pressure is low in the present invention,evaporation is inevitably caused at a gas-liquid equilibrium compositionunder conditions of temperature and pressure given in individual cases.The evaporation gas becomes a distillate composed mainly of benzene andthe volume of the gas is determined by the balance between the quantityof the generated heat of reaction and the quantity of heat removed asthe sensible heat of the liquid, depending on the reaction conditionssuch as the reaction pressure, the feed rates of the starting materials,the heat of reaction, the preheating temperature of the startingmaterials, etc. Therefore, the maximum attained temperature of thecatalyst layer can be controlled to be an arbitrary constant temperatureby removing some of the large heat of reaction generated with theprogress of alkylation, as the latent heat for evaporation to suppressthe rise of the reaction temperature. This control is effective insuppressing the deterioration of the catalyst and maintaining theselectivity.

The reactive materials in the present invention are benzene and ethyleneused as an alkylating agent. The distillate composed mainly of unreactedbenzene which is recovered as vapor in order to remove the heat ofreaction can be reused as a reactive material.

Benzene used as starting material in the present invention is preferablyfreed of water to have a water content of 200 ppm or less for thepurpose of preventing a decrease of the catalytic activity caused by theadsorption of water on the catalyst in a low temperature region.

As ethylene used as starting material in the present invention, therecan be used not only purified ethylene gas but also crude ethylene gas(containing, for example, paraffin hydrocarbon gases such as methane andethane, propylene, and hydrogen) produced in a conventional naphthacracker.

The process of the present invention is characterized in that thereaction can be carried out in a gas-liquid mixed phase. Therefore, thereaction can be carried out under a relatively low pressure also whenthe crude ethylene gas is used as starting material. On the other hand,a process requiring complete dissolution of ethylene in benzene asbefore is not practical because a very high pressure is necessary fordissolving ethylene when starting crude ethylene gas is used.Accordingly, the process of the present invention is desirable from anindustrial viewpoint because a step of purifying starting ethylene canbe omitted.

The benzene/ethylene molar ratio of a reactive gas fed in the presentinvention (hereinafter referred to as "benzene/ethylene feeding molarratio" or merely as "feeding molar ratio") is 1 to 6, preferably 1.5 to4, more preferably 2 to 3.

In the present invention, since a portion of unreacted benzene isrecovered as vapor, the product solution has a benzene ring/ethyl groupmolar ratio lower than the feeding molar ratio. When the evaporation gasdistillate is reused by recycling and feeding the gas to the reactor asdescribed above, there can be obtained a product solution having thesame benzene ring/ethyl group molar ratio as the feeding molar ratio.The benzene ring/ethyl group molar ratio of the product solution ispreferably 1 to 3 for maintaining a high selectivity. Therefore, whenthe evaporation gas distillate is reused by recycling and feeding thegas to the reactor, the adjustment of the benzene/ethylene feeding molarratio of the reactive gas to be fed to 1 to 3 is sufficient to attain abenzene ring/ethyl group molar ratio of the product solution of 1 to 3.

The reaction pressure in the present invention is determined by thepartial pressure of the evaporation gas composed mainly of benzene whichis determined by gas-liquid equilibrium, depending on the composition ofa desired product solution, the benzene/ethylene feeding molar ratio,the maximum attained temperature of the catalyst layer, etc. It isusually preferable to adjust the maximum attained temperature of thecatalyst layer (i.e. the gas-liquid equilibrium temperature) to 250° C.or lower for maintaining the selectivity of nuclear ethylation. Thepressure is determined so that boiling may occur at 250° C. or lower tocause concentration of the product solution. When the reaction pressureis too low, it is feared that the reaction rate is decreased and thatthe degree of evaporation, i.e., the degree of recycling is increased.Therefore, as to a preferable pressure, the partial pressure of theproduced vapor distillate composed mainly of benzene is 5 to 20 kg/cm²G, preferably 10 to 15 kg/cm² G for attaining a sufficient reaction rateand keeping the composition and flow rate of the product solution to berecovered and the composition and the flow rate of the vapor to berecycled, in practical ranges.

When crude ethylene is used as starting material, gas components otherthan the olefin component such as ethylene or propylene, which isconsumed in the alkylation are discharged into the gas phase togetherwith the vapor distillate composed mainly of benzene. Therefore, forestablishing the same evaporation gas-liquid equilibrium as in the caseof using pure ethylene, the reaction is carried out at an operatingpressure corrected for the partial pressure. The operating pressureshould be determined by considering the purity of ethylene.

The reaction temperature in the present invention is defined as themaximum attained temperature of the catalyst layer. It is determined bythe reaction pressure and the composition of the liquid and ispreferably 170-250° C. for maintaining sufficient reaction rate andselectivity. The reaction pressure is properly chosen as described aboveso that the reaction temperature may fall in the above range. Therefore,the reaction temperature is raised to a desired temperature by the heatof reaction. However, since the whole of the residual heat of reactionis used for evaporating the distillate composed mainly of benzene, thetemperature of the catalyst layer can be kept constant.

In the present invention, the temperature of the catalyst layer at itsinlet (the benzene preheating temperature) is set at a temperature atleast 50° C. lower than the above-mentioned maximum attained temperatureof the catalyst layer. The reason is as follows: keeping the temperatureof the catalyst layer at the inlet low increases the solubility ofethylene at the inlet of the catalyst layer and hence contributesgreatly to the complete conversion of ethylene; and it gives atemperature profile of the catalyst layer from the temperature at theinlet to the maximum attained temperature, i.e., the boiling pointattained under predetermined conditions, so as to further lower theaverage temperature of the catalyst layer, and hence it is effective inmaintaining a high selectivity. Since the decrease of the catalyticactivity in the vicinity of the inlet of the catalyst layer whereethylene bubbles are substantially present is dependent on temperature,the temperature of the catalyst layer at its inlet is preferably as lowas possible also from the viewpoint of preventing the decrease of theactivity. The actual preheating temperature (the temperature of thecatalyst layer at its inlet) in the present invention is determined inview of the composition of a desired product solution (the volume of theevaporation gas). As a temperature at which the reaction is initiated,the actual preheating temperature is 30° C. or higher and chosen so asto be 50° C. or more lower than the maximum attained temperature of thecatalyst layer, and it is preferably 30-200° C., more preferably 80-160°C.

Thus, in the present invention, the temperature of the catalyst layer islowest at the inlet of the catalyst layer and rises with a decrease ofthe distance to the top of the catalyst layer owing to heat generationcaused by the progress of the reaction. When the temperature reaches apredetermined temperature, evaporation takes place and the heat ofreaction is removed as the latent heat of evaporation, so that thetemperature does not rise any more. Since the catalyst layer has apredetermined temperature profile, keeping the temperature of thecatalyst layer at the inlet low increases the solubility of ethylene atthe inlet of the catalyst layer and hence contributes to the increase ofthe reaction rate and the complete conversion of ethylene. According tothe present invention, even if ethylene bubbles are present at the inletof the catalyst layer, an effect of suppressing the decrease of thecatalytic activity can be obtained by keeping said layer at a lowtemperature. Such a temperature profile of the catalyst layer means alowering of the average temperature of the whole catalyst layer, andthis lowering is effective in maintaining the selectivity of nuclearethylation at a very high value.

Under the conditions of a low benzene/ethylene feeding molar ratio and alow pressure which are employed in the present invention, ethylene fedcannot, as a matter of course, be completely dissolved in benzene at theinlet of the catalyst layer and is present as bubbles. Conventionalprocesses involve, for example, the following problems: in the abovesituation, the deterioration of the catalyst and the decrease of theselectivity become remarkable and the temperature is raised by the largeheat of reaction. In the conventional processes, for avoiding theseproblems, the reaction is carried out at a high benzene/ethylene molarratio at which ethylene is completely dissolved in benzene, and forobtaining a product having a low benzene ring/ethyl group molar ratio,there is no choice but to adopt a very troublesome reaction method.However, surprisingly, according to the present invention, thealkylation at a low benzene/ethylene molar ratio can be carried out witha very simple apparatus under a low pressure. Therefore, the alkylationcan be carried out even by using starting ethylene of low purity, sothat an ethylene purification step can be omitted.

The present inventors found for the first time that a β zeolite isexcellent in resistance to deterioration caused by its contact withgaseous ethylene and can exhibit a high catalytic activity and a highreaction selectivity even at a low benzene/ethylene molar ratio. On thebasis of this finding, the inventors made it possible to maintain thetemperature of a catalyst layer at an arbitrary temperature by using theβ zeolite as catalyst and removing some of the generated heat ofreaction by evaporating a distillate composed mainly of unreactedbenzene. Thus, the inventors found a process which permits completion ofthe alkylation (complete conversion of ethylene) with high selectivityeven at a low benzene/ethylene molar ratio. Furthermore, in the processof the present invention, the decrease in activity of the catalyst isvery slight.

The present invention is explained with reference to examples. Thepresent invention is not limited to the examples and variousalternations and modifications can be made within the scope of gist ofthe invention.

EXAMPLE 1

Synthesis of a β Zeolite

160 Grams of a 10% aqueous tetraethylammonium hydroxide solution, 140 gof water, 4.2 g of sodium hydroxide and 9.5 g of sodium aluminate NaAlO2were mixed to effect dissolution, followed by adding thereto 70.5 g offused silica "Nipsil" (a trade name of NV-3, mfd. by Nippon SilicaIndustrial Co., Ltd.) and 7 g of a β zeolite as a seed crystal, and theresulting mixture was stirred for 30 minutes in a homogenizer at a rateof 5,000 rotations per minute. Then, the mixture was placed in a 500-mlautoclave and allowed to stand at 155° C. for 8 days without stirring togive a large amount of a crystalline substance. This substance wasfiltered, washed with water and then dried at 120° C. for 24 hours toobtain 66 g of crystalline powder. Subsequently, the crystalline powderwas slowly heated to 350-550° C. and finally calcined at 550° C. for 6hours. The calcined powder was confirmed to be β zeolite by X-raydiffraction.

Hydrogen Ion Exchange of the β Zeolite

To 450 g of a 0.15N aqueous nitric acid solution was added 50 g of thecalcined β zeolite, and the resulting mixture was stirred at roomtemperature for 3 hours to carry out ion exchange. After the exchange,the exchange product was filtered, washed with water and then dried at120° C. to obtain hydrogen ion type β zeolite. The composition of thiszeolite was analyzed with a X-ray microanalyzer (EPMA). Thesilica/alumina ratio was 25. Synthesis and hydrogen ion exchange ofzeolite were carried out several times by the same procedures asdescribed above. Some of the thus obtained hydrogen ion type β zeolitewas shaped into tablets of 3 mmφ×3-5 mmL with a tablet machine. Byrepeating the same procedure as described above, 400 g of shapedcatalyst was obtained.

Alkylation Experiment

400 Grams of the above-mentioned shaped product of zeolite β catalystwas packed into a stainless-steel reaction tube with an inside diameterof 42.8 mm and a length of 1,500 mm equipped with a heating mediumjacket as a preheating layer around the lower region of the reactor fromthe bottom to a height of 600 mm, a pressure control valve at the outletof the reactor, and an overflow nozzle for taking out a product solutionwhich was located below the pressure control valve. The catalyst packingregion was a region between heights of 600 mm and 1,320 mm from thebottom of the reactor, and a stainless-steel Dickson packing of 3 mmφwas packed over and under the catalyst layer. The nozzle for taking outa product solution was connected to a solution recovery drum which hadbeen pressurized with nitrogen so as to be equal to the reactor ininternal pressure. At the outlet of the reactor, an evaporation gasdistillate was recovered from the pressure control valve through acondenser, and the liquid was recovered as a product solution into thesolution recovery drum through the nozzle for taking out a productsolution.

Benzene was fed at a feed rate of 2,280 g/Hr through the bottom of thereactor (the inlet of the preheating layer). The internal pressure ofthe reactor was adjusted to 13.8 kg/cm2G with the pressure control valveat the outlet of the reactor to make the inside of the system completelyliquid-sealed. A heating medium kept at 150° C. was circulated in theheating medium jacket provided as preheating layer, to adjust thetemperature of the catalyst layer at its inlet to 122° C. Then, likebenzene, ethylene was fed through the bottom of the reactor at a feedrate of 10.18 mol/Hr to initiate the reaction. After the initiation ofthe reaction, the temperature of the catalyst layer rose slowly and themaximum attained temperature of the catalyst layer reached 230° C. inthe middle region of the catalyst layer. Since partial evaporation wascaused under the reaction conditions employed in the present example, afurther temperature rise was inhibited and the temperature of 230° C.was maintained also in the upper part of the catalyst layer. Thetemperature at the overflow nozzle position (the liquid level position)was 222° C. The benzene/ethylene feeding molar ratio was 2.87. It wasclear that under such conditions, the ethylene fed could not becompletely dissolved in benzene, so that ethylene bubbles were presentat the inlet of the catalyst layer.

The product solution was obtained at a rate of 1,572 g/Hr in such aconcentrated state that its benzene ring/ethyl group molar ratio was2.14. The selectivity of nuclear ethylation products was 99.7%. Theevaporation gas distillate was obtained at a rate of 992 g/Hr and had abenzene ring/ethyl group molar ratio of 6.06. The conversion of ethylenewas 99.97%, namely, ethylene was substantially completely converted. Thereaction was continued for 500 hours. Based on the tendency of change ofthe temperature profile of the catalyst layer (in particular, thetemperature change near the inlet of the catalyst layer), the decreaseof the catalytic activity was found to proceed slowly. The conversion ofethylene, however, did not show at all a tendency of decreases, namely,substantially complete conversion was achieved. The results obtained areshown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Operation time (Hr)     50     100    500                                       Temperature (° C.)                                                     Inlet of catalyst layer 122 121 122                                           Maximum attained temperature of catalyst layer 230 230 230                    Position of nozzle for taking out product solution 222 222 222                Reaction pressure (kg/cm.sup.2 G) 13.81 13.82 13.81                           Feed of materials                                                             (mol/Hr)                                                                      Benzene 29.23 29.23 29.23                                                     Ethylene 10.18 10.18 10.18                                                    Feeding molar ratio benzene/ethylene 2.87 2.87 2.87                           Product solution                                                              Recovery rate (g/Hr) 1572 1577 1574                                           Composition (wt %)                                                            Benzene 53.12 53.06 53.06                                                     Ethylbenzene 34.88 35.01 35.11                                                Diethylbenzene 10.16 10.07 10.09                                              Triethylbenzene 1.64 1.69 1.58                                                Benzene ring/ethyl group 2.14 2.14 2.14                                       Selectivity of nuclear ethylation 99.72 99.75 99.75                         ______________________________________                                    

    ______________________________________                                        Evaporation gas                                                                 Recovery rate (g/Hr) 992 989 991                                              Composition (wt/%)                                                            Benzene 80.06 80.10 80.12                                                     Ethylbenzene 17.94 17.92 17.90                                                Diethylbenzene 1.84 1.83 1.82                                                 Triethylbenzene 0.14 0.14 0.14                                                Benzene ring/ethyl group 6.06 6.08 6.09                                       Selectivity of nuclear, ethylation 99.94 99.92 99.94                          Conversion of ethylene (%) 100.00 99.96 99.96                               ______________________________________                                    

From the present example, the following can be seen: according to theprocess of the present invention, the alkylation at a lowbenzene/ethylene molar ratio is completed with high selectivity even ifethylene bubbles are clearly present at the inlet of the catalyst layer;the heat of reaction can be removed because a portion of unreactedbenzene is recovered as vapor; there can be obtained a product having abenzene/ethyl group molar ratio of as very low as about 2; and thedecrease in activity of the catalyst is very slight. In the presentexample, the production rate (in terms of ethylbenzene) relative to theweight of the catalyst was 2.7 g-ethylbenzene/g-catalyst/hour.

EXAMPLE 2

A β zeolite (sodium type) mfd. by PQ Corporation was converted to ahydrogen ion type under the same conditions as in Example 1 to obtainhydrogen ion type β zeolite. The silica/alumina ratio of the hydrogenion type β zeolite obtained was 35.

The hydrogen ion type β zeolite obtained was shaped into tablets of 3mmφ×3-5 mmL with a tablet machine. The same procedure as described abovewas repeated to obtain 400 g of shaped catalyst.

The same reactor as in Example 1 was packed with 400 g of the catalyst.The height of the packing layer was 725 mm. Benzene was fed at a feedrate of 2,400 g/Hr through the bottom of the reactor (the inlet of thepreheating layer). The internal pressure of the reactor was adjusted to13.8 kg/cm² G with the pressure control valve at the outlet of thereactor to make the inside of the system completely liquid-sealed. Aheating medium kept at 160° C. was circulated in the heating mediumjacket provided as preheating layer, to adjust the temperature of thecatalyst layer at its inlet to 133° C. Then, like benzene, ethylene wasfed through the bottom of the reactor at a feed rate of 10.71 mol/Hr toinitiate the reaction. After the initiation of the reaction, thetemperature of the catalyst layer rose slowly and the maximum attainedtemperature of the catalyst layer reached 232° C. in the middle regionof the catalyst layer. It was clear that at such a temperature and apressure, a portion of the reaction solution was evaporated in thereactor. The evaporation gas distillate was introduced into the recoverydrum containing benzene previously placed therein. The level in the drumis controlled to be constant and the liquid introduced into the drum wasrecycled to a starting-material line (a feed materials mixing tank) witha pump. On the other hand, benzene was fed to said tank so that thetotal volume of liquids fed to the reactor might be constant, namely,the liquid level in the feed materials mixing tank might be keptconstant.

After several hours, the system became stable and the recycling flowrate, the benzene feed flow rate and the product solution recovery flowrate became substantially constant values of 1,042 g/Hr, 1,362 g/Hr and1,662 g/Hr, respectively. In this case, the maximum temperature of thecatalyst layer was 232° C., its temperature at the product recoverynozzle was 230° C., and the reaction pressure was 13.8 kg/cm2G. Thereaction was continuously carried out for 500 hours. The resultsobtained are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Operation time (Hr)   100     309     500                                       Temperature (° C.)                                                     Inlet of catalyst layer 131 133 131                                           Maximum attained temperature of catalyst 232 232 231                          layer                                                                         Position of nozzle for taking out product 230 230 230                         solution 230 230 230                                                          Reaction pressure (kg/cm.sup.2 G) 13.81 13.81 13.81                           Feed of materials                                                             (mol/Hr)                                                                      Feeding molar ratio                                                           Benzene 17.46 17.46 17.46                                                     Ethylene 10.71 10.71 10.71                                                    Benzene/ethylene 1.63 1.63 1.63                                               Recycling                                                                     Flow rate of liquid (g/Hr) 1042 1028 1044                                     Benzene ring/ethyl group 4.10 4.09 4.11                                       Product solution                                                              Recovery rate (g/Hr) 1661 1676 1659                                           Composition (wt %)                                                            Benzene 41.10 41.22 41.10                                                     Ethylbenzene 43.33 43.30 43.28                                                Diethylbenzene 13.11 13.01 13.21                                              Triethylbenzene 2.00 2.04 1.99                                                Others* 0.45 0.42 0.43                                                        Benzene ring/ethyl group 1.62 1.63 1.63                                       Selectivity of nuclear ethylation 99.57 99.61 99.61                           Conversion of ethylene (%) 99.96 99.96 99.94                                ______________________________________                                         *Others: tetraethylbenzene, butylbenzene, diphenylethane, etc.           

In the present example, the benzene/ethylene feeding molar ratio understeady state conditions was 1.63, the benzene ring/ethylene molar ratiowas 2.78 even when the recycled liquid was added, and ethylene bubbleswere clearly present at the inlet of the catalyst layer. A productsolution having a benzene ring/ethyl group molar ratio of 1.62 wasobtained over 500 hours. Thus, it can be seen that ethylene wassubstantially completely converted. The production rate (in terms ofethylbenzene) relative to the weight of the catalyst was 2.84g-ethylbenzene/g-catalyst/hour. Furthermore, during the production, theselectivity of nuclear ethylation in the case of the product solutionwas maintained at a very high value of 99.6%.

EXAMPLE 3

Reaction,was carried out using the following mixed gas as startingethylene (percents are by volume):

    ______________________________________                                        Ethylene        44.19%                                                          Methane 35.32%                                                                Ethane 4.44%                                                                  Propylene 0.04%                                                               Hydrogen 15.94%                                                               Carbon monoxide 0.07%                                                       ______________________________________                                    

The same zeolite β catalyst shaped product and reaction apparatus as inExample 2 were used. However, in the present example, since the startingmaterial contained inert gases such as methane and hydrogen, a gas phasepressure equalization line was provided in a gas phase recoveringreceiver and a product solution recovering receiver and these receiverswere equalized in internal pressure.

Benzene was fed at a feed rate of 2,400 g/Hr through the bottom of thereactor (the inlet of the preheating layer). The internal pressure ofthe reactor was adjusted to 30.2 kg/cm2G with the pressure control valveat the outlet of the reactor to make the inside of the system completelyliquid-sealed. At the operating pressure in the present example, theinert gases (hydrogen, methane, ethane and a slight volume of carbonmonoxide gas) were exhausted to the gas phase recovery side. Therefore,for evaporating a starting mixed gas containing the same components inthe same proportions as in Example 2, it was necessary to correct thetotal pressure in view of the partial pressures of the inert gases.Accordingly, the operating pressure was adjusted to 30.2 kg/cm² G.

A heating medium kept at 160° C. was circulated in the heating mediumjacket provided as preheating layer, to adjust the temperature of thecatalyst layer at its inlet to 132° C. Then, like benzene, the startingmixed gas containing ethylene was fed through the bottom of the reactorat a feed rate of 24.25 mol/Hr (10.71 mol/Hr in terms of ethylene) toinitiate the reaction. After the initiation of the reaction, thematerial feed rates were controlled in the same manner as in Example 2,and the system assumed a steady state after several hours. The recyclingflow rate, the benzene feed flow rate and the product solution recoveryrate became substantially constant values of 1,043 g/Hr. 1,362 g/Hr and1,662 g/Hr, respectively. The reaction was continuously carried out for500 hours. The results obtained are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Operation time (Hr)       300     500                                           Temperature (° C.)                                                     Inlet of catalyst layer 131 131                                               Maximum attained temperature of catalyst layer 230 230                        Position of nozzle for taking out product solution 230 230                    Reaction pressure (kg/cm.sup.2 G) 30.15 30.14                                 Feed of materials                                                             (mol/Hr) Feeding                                                              molar ratio                                                                   Benzene 17.46 17.46                                                           Feed rate of the whole gas 24.25 24.25                                        Ethylene 10.71 10.71                                                          Benzene/ethylene 1.63 1.63                                                    Recycling                                                                     Flow rate of liquid 1033 1030                                                 Benzene ring/ethyl group 4.10 4.09                                            Product solution                                                              Recovery rate (g/Hr) 1663 1666                                                Composition (wt %)                                                            Benzene 41.07 41.06                                                           Ethylbenzene 43.32 43.36                                                      Diethylbenzene 13.15 13.12                                                    Triethylbenzene 2.00 2.00                                                     Others* 0.47 0.46                                                             Benzene ring/ethyl group 1.62 1.62                                            Selectivity of nuclear ethylation 99.53 99.53                                 Convention of ethylene (%) 99.96 99.94                                      ______________________________________                                         *Others: tetraethylbenzene, cumene, butylbenzene, diphenylethane, etc.   

From the present example, the following can be seen: in 500 hours,ethylene was completely converted, the benzene ring/ethyl group ratio ofthe product solution was maintained at 1.62, and the selectivity ofnuclear ethylation was maintained at 99.5% for the product solution. Inthis case, the production rate (in terms of ethylbenzene) relative tothe weight of the catalyst was 2.84 g-ethylbenzene/g-catalyst/hour. Fromthe present example, it can also be seen that the alkylation can becarried out using starting ethylene of low purity because ethylene neednot be completely dissolved unlike in conventional processes.

Comparative Example 1

This comparative example was carried out for comparing reaction resultsobtained by using each of a Y type zeolite and a zeolite β catalyst.

Stainless-steel reaction tube with an inside diameter of 22.1 mm and alength of 800 mm equipped with a heating medium jacket as a preheatinglayer around the lower region of the reactor from the bottom to a heightof 300 mm and a pressure control valve at the outlet of the reactor, waspacked with 30 g of particles which had been prepared by grounding ashaped product of hydrogen ion type zeolite β catalyst obtained in thesame manner as in Example 1, followed by classification and particlesize regulation to 8 to 14 mesh. The catalyst packing region was aregion between heights of 320 mm and 510 mm from the bottom of thereactor, and a stainless-steel Dickson packing of 3 mmφ was packed overand under the catalyst layer. Benzene was fed at a feed rate of 319 g/Hrthrough the bottom of the reactor (the inlet of the preheating layer).The internal pressure of the reactor was adjusted to 13.5 kg/cm² G withthe pressure control valve at the outlet of the reactor to make theinside of the system completely liquid-sealed. A heating medium kept at140° C. was circulated in the heating medium jacket provided aspreheating layer, to adjust the temperature of the catalyst layer at itsinlet to 135° C. Then, like benzene, ethylene was fed through the bottomof the reactor at a feed rate of 1.4 mol/Hr to initiate the reaction.The maximum attained temperature of the catalyst layer reached 232° C.in the middle region of the catalyst layer, but since partialevaporation was caused under the reaction conditions employed in thepresent comparative example, a further temperature rise was inhibitedand the temperature of 232° C. was maintained also in the upper part ofthe catalyst layer. A condenser was provided at the outlet of thereactor and the whole products were recovered as a liquid, which wasanalyzed by a gas chromatography.

Next, the same experiment as above was carried out except for using ashaped product of 8 to 14 mesh of Y type zeolite LZY-82 (a trade name,mfd. by Linde Zeolite Co.) as a catalyst. The amount of the catalystpacked was 33.3 g and the catalyst layer region was a region betweenheights of 320 mm and 470 mm from the bottom of the reactor. Thetemperature of the catalyst layer at its inlet was adjusted to 145° C.and the reaction was initiated. Table 5 shows the comparison of thereaction results obtained by using each of the Y type catalyst and the βtype catalyst.

                  TABLE 5                                                         ______________________________________                                        Catalyst          H-β     LZY-82                                           Packing amount (g) 30 33.33                                                   Feed of materials                                                             Benzene 4.09 4.09                                                             Ethylene (mol/H) 1.41 1.38                                                    BZ/EY molar ratio 2.91 2.96                                                 Reaction time (Hr)                                                                              3      15     30   1    4                                     Temperature                                                                   Inlet of catalyst layer 135 135 135 145 145                                   Exit end of catalyst layer (° C.) 232 232 232 206 199                  Composition of                                                                solution (wt %)                                                               Benzene 63.1 63.1 63.1 76.6 79.4                                              Ethylbenzene 29.3 29.3 29.3 18.2 15.5                                         Diethylbenzene 6.5 6.5 6.5 3.0 2.7                                            Triethylbenzene 0.9 0.9 0.9 0.7 0.7                                           Others* 0.2 0.2 0.2 1.5 1.7                                                   Benzene ring/ethyl group molar ratio 2.91 2.91 2.91 4.78 5.38                 Selectivity of nuclear ethylation (%) 99.68 99.68 99.68 95.42 93.87                                                    Conversion of ethylene (%)                                                   99.26 99.22 99.54 73.0 60.2         ______________________________________                                         *Others: tetraethylbenzene, cumene, butylbenzene, diphenylethane, etc.   

The benzene/ethylene feeding molar ratio was 2.9, and at the inlet ofthe catalyst layer, ethylene was not completely dissolved in benzene andethylene bubbles were present.

When the β zeolite was used as a catalyst, the conversion of ethylenewas 99.3%, namely, ethylene was substantially completely converted, andthe selectivity of nuclear ethylation products was as very high as99.7%. Moreover, these values were maintained for 30 Hr, namely, theactivity was not deteriorated at all.

On the other hand, when the Y type zeolite was used as a catalyst, theselectivity of nuclear ethylation products was as very low as 95.5% andthe conversion of ethylene was only 73% even in the early stages andfell down to 60% in only 4 hours of the reaction.

From the present comparative example, it can be seen that Y typezeolites widely used in conventional processes cannot be used at such avery low benzene/ethylene molar ratio as is employed in the presentinvention.

Comparative Example 2

The present comparative example was carried out for comparing reactionresults obtained by employing different catalyst layer temperatureprofiles.

The same reaction apparatus as used in Comparative Example 1 was packedwith 30 g of particles which had been prepared by grounding a shapedproduct of hydrogen ion type zeolite β catalyst obtained in the samemanner as in Example 1, followed by classification and particle sizeregulation to 8 to 14 mesh. The catalyt packing region was a regionbetween heights of 320 mm and 510 mm from the bottom of the reactor, anda stainless-steel Dickson packing of 3 mmφ was packed over and under thecatalyst layer. Benzene was fed at a feed rate of 319 g/Hr through thebottom of the reactor (the inlet of the preheating layer). The internalpressure of the reactor was adjusted to 13.8 kg/cm² G with the pressurecontrol valve at the outlet of the reactor to make the inside of thesystem completely liquid-sealed. A heating medium at 230° C. wascirculated in the heating medium jacket provided as heating layer, toadjust the temperature of the catalyst layer at its inlet to 195° C.Then, like benzene, ethylene was fed through the bottom of the reactorat a feed rate of 1.4 mol/Hr to initiate the reaction. The maximumattained temperature of the catalyst layer reached 232° C. in the middleregion of the catalyst layer, but since partial evaporation was causedunder the reaction conditions employed in the present comparativeexample, a further temperature rise was inhibited and the temperature of232° C. was maintained also in the upper part of the catalyst layer. Asin Comparative Example 1, a condenser was provided at the outlet of thereactor and the whole products were recovered as a liquid, which wasanalyzed by a gas chromatography. Table 6 shows the results ofevaluating the reaction.

                  TABLE 6                                                         ______________________________________                                        Catalyst               H- β                                                Packing amount (g) 30                                                       Feed of    Benzene         4.09                                                 materials Ethylene (mol/H) 1.41                                                BZ/EY molar ratio 2.91                                                     Reaction time (Hr)     10      30                                             Temperature                                                                              Inlet of catalyst layer                                                                       195     195                                           Exit end of catalyst layer 233 232                                            (° C.)                                                                Composition Benzene 63.43 64.23                                               of solution Ethylbenzene 29.16 28.71                                           Diethylbenzene 6.33 6.08                                                      Triethylbenzene 0.73 0.67                                                     Others * 0.36 0.32                                                         Benzene ring/ethyl group molar ratio                                                                 2.95    3.03                                             Selectivity of nuclear ethylation (%) 99.34 99.38                             Convertion of ethylene (%) 98.3 95.6                                        ______________________________________                                    

Others: tetraethylbenzene, cumene, butylbenzene, diphenylethane, etc.

As described in Comparative Example 1, when the temperature of thecatalyst layer at its inlet was adjusted to 135° C., the conversion ofethylene was 99.3%, namely, ethylene was substantially completelyconverted, and the selectivity of nuclear ethylation products was asvery high as 99.7%. Moreover, these values were maintained for 30 Hr,namely, the activity was not deteriorated at all. On the other hand, thefollowing became apparent: when as in the present comparative example,the temperature of the catalyst layer at its inlet was 195° C. which wasremarkably out of the temperature range specified in the presentinvention, i.e., the temperature range of 50° C. or more lower than themaximum attained temperature of the catalyst layer, the conversion ofethylene was 98% even in the early stages, namely, ethylene was notcompletely converted; the selectivity of nuclear ethylation was as lowas 99.3%; and moreover the deterioration of the catalytic activity wasrelatively rapid. When the industrial production of ethylbenzene isconsidered, such a catalyst layer temperature profile is not preferablebecause it extremely increases the flow rate (recycling rate) of theevaporation gas and hence decreases the recovery rate of the productsolution.

INDUSTRIAL APPLICABILITY

According to the present invention, alkylation of benzene can be carriedout at a very low benzene/ethylene feeding molar ratio withoutdecreasingthe catalytic activity, while maintaining a very highselectivity of nuclear ethylation and complete conversion of ethylene.Furthermore, the reaction can be carried out with a simple apparatusunder a low pressure. In addition, since complete dissolution ofethylene is not necessary unlike in conventional processes, the reactioncan be carried out using starting ethylene of low purity. These factsare very advantageous for the industrial production of ethyl-benzene.

Relation to Other Applications

The present application is based on Japanese Patent Application No.08-207567 filed on Jul. 19, 1996 and the contents thereof areincorporated as a whole into the present specification by reference.

We claim:
 1. A process for producing ethylated benzene by a reaction ofbenzene with ethylene in the presence of a catalyst containing a zeoliteβ by using a fixed-bed ascending-flow reactor, which comprisesa)carrying out the reaction under conditions under which ethylene bubblesare present at the inlet of a catalyst layer when ethylene is fed upwardfrom under the catalyst layer, b) recovering reaction products as aliquid from the upper part of the reactor and at the same time takingout a distillate composed mainly of unreacted benzene therefrom asvapor, and c) adjusting the temperature of the catalyst layer at itsinlet to a temperature at least 50° C. lower than the maximum attainedtemperature of the catalyst layer.
 2. A process for producing ethylatedbenzene according to claim 1, wherein the feeding molar ratio of benzeneto ethylene is 1 to
 6. 3. A process for producing ethylated benzeneaccording to claim 1, wherein the benzene ring/ethyl group molar ratioof the product solution obtained is 1 to
 3. 4. A process for producingethylated benzene according to claim 1, which employs such a catalystlayer temperature profile that the temperature of the catalyst layer atits inlet is 30-200° C. and the maximum attained temperature of thecatalyst layer is 170-250° C.
 5. A process for producing ethylatedbenzene according to claim 1, wherein the partial pressure of thedistillate taken out as vapor from the upper part of the reactor is 5 to20 kg/cm² G.
 6. A process for producing ethylated benzene according toclaim 1, wherein the distillate composed mainly of unreacted benzenewhich is recovered as vapor from the reactor is recycled and fed to thereactor.
 7. A process for producing ethylated benzene according to claim6, wherein the feeding molar ratio of benzene to ethylene is 1 to 3.